Cbird

I have a 2001 Mustang GT (5speed) that makes a super high pitched whistle whenever I push it, or give it a decent amount of throttle, but it's only at a certain throttle position + load. When I hear the squeal if I let off the throttle it goes away. Like-wise if I push the throttle down a little more it also goes away. It sounds just like brake pads squealing. It's a constant noise, it's not like a rhythmic chirp or squeak.

It won't do it in neutral though. That's what makes diagnosing this so hard. It's gotten progressivly worse. I first noticed it only going up-hill (heavy load, I suppose was the deciding factor) now I can hear it just about any time I give it some gas OR when I let off the gas it will squeak just as it hits that "magic" throttle position as the valve closes.

Things I've tried:
Idler pulleys/Belt tensioner/ serp belt
new air filter
new pcv valve
checked main vac lines for obvious wear and tear (found one leak but that wasn't it, sadly)
changed radiator cap
Smoke tested the vac lines (noticed quite a bit of smoke coming out of the egr valve, possibly normal since I was blowing throttle body side not the normal way that flows)
replaced passenger side exhaust flange gasket
put the stock air box back on
Monitored short term fuel trims while driving to look for discrepancies. No changes squealing vs not squealing.

I'm out of ideas. It wouldn't be a big deal except it's really loud. I notice when I try to roll both windows up at the same time the car stalls a little and the headlights dim quite a bit. Could it be my alternator is going out? I suppose it would make the sound when revving in neutral to then wouldn't it?

I also noticed when I took the IAC valve hose off and blew into it I would hear a whistle sound coming from the throttle body BUT when I plugged that little hole in the butterfly valve it stopped. Don't know if that an issue or not.

Any ideas?

Cbird

I think it's a bearing. Either Trans of accessory. Does anyone have any tips on how to diagnose from here?

Stevo86

If it only happens when you're moving it's driveline related not necessarily engine related. Kind of sounds like something has torn itself up in the rear end or possibly in the transmission.

A rear end that is going bad and gotten itself out of alignment may only make noise in the push side and not the decel side. It happens.

Cbird

It sounds to me like it's coming from the front passenger side. However, If I roll the driver window down it sounds like it's coming from the driver side.

Could it be possible a pilot or throw out bearing?

At idle I can hear a random tick and squeak now. It's much softer then when I'm driving though so maybe that's just cold weather related?

I'm thinking maybe I should just live with it until it gets worse/easier to diagnose/causing drivability issues. What do you think? Does it sound like just a quirk?